Climate change-driven increases in drought frequency and severity could compromise forest ecosystems and the terrestrial carbon sink^1,2,3. While the impacts of single droughts on forests have been widely studied^4,5,6, understanding whether forests acclimate to or become more vulnerable to sequential droughts remains largely unknown and is crucial for predicting future forest health. We combine cross-biome datasets of tree growth, tree mortality and ecosystem water content to quantify the effects of multiple droughts at a range of scales from individual trees to the globe from 1900 to 2018. We find that subsequent droughts generally have a more deleterious impact than initial droughts, but this effect differs enormously by clade and ecosystem, with gymnosperms and conifer-dominated ecosystems more often exhibiting increased vulnerability to multiple droughts. The differential impacts of multiple droughts across clades and biomes indicate that drought frequency changes may have fundamentally different ecological and carbon-cycle consequences across ecosystems.

由气候变化驱动的干旱频率和严重性增加可能会损害森林生态系统和陆地碳汇^1,2,3。尽管已经广泛研究了单一干旱对森林的影响^4,5,6，了解森林是否适应连续干旱还是变得更容易遭受干旱仍然是未知的，并且对于预测未来的森林健康至关重要。我们结合了树木生长，树木死亡率和生态系统含水量的跨生物学组数据集，以量化从1900年到2018年从单个树木到全球范围内多次干旱的多重影响。我们发现随后的干旱通常具有更有害的影响与初次干旱相比，这种影响在进化枝和生态系统中有很大的不同，裸子植物和以针叶树为主的生态系统更容易表现出对多种干旱的脆弱性。进化枝和生物群落之间多次干旱的不同影响表明，干旱频率变化可能对整个生态系统具有根本不同的生态和碳循环后果。